TART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. V. 



621 



In this paper we find a very interesting table of collected results from observations of Gegenschein 

 U various stations by BRORSEN, SCHMIDT, HEIS, EYLERT, BUSCH, GRONEMAN, BACKHOUSE, LEWIS, BARNARD, 

 ind at Harvard College. 



TABLE CV1I. 



The first line gives the total number of observations. 



The other five lines give the longitude, its excess over that of the point in opposition to the 

 ,un, and the latitude, of the observed light, with its extent in longitude and latitude, so far as this can 

 >e estimated by means of the sketches or descriptions. These quantities are given only in entire 

 tegrees. 



From northern stations, it appears from the table that Gegenschein has most frequently been seen 

 n October, but the number of observations in February and March is also relatively large. According to 

 xperience at the Harvard College Observatory, the phenomenon to be observed is often difficult to 

 listinguish, in March, from a part of the luminous band crossing the ecliptic nearly at right angles on 

 he borders of LEO and VIRGO, while in October, as in the other autumn months, it is perceptible only 

 s a reinforcement or as an extension of the band from Aquila to the Pleiades. 



During February and March the observed light has a position a few degrees preceding the point 

 n opposition to the sun, generally north of the ecliptic. 



In the autumn of 1886 the general remarks made by BARNARD and those made at Harvard Obser- 

 atory concur in describing Gegenschein as only a very elongated patch of light, instead of a round or 

 lliptical spot. 



BRORSEN'S above-quoted observations may thus in the main be said to be confirmed by all subse- 

 [uent researches. 



We shall now see that these results of observations of counter-glow (Gegenschein) in nature can be 

 xplained by the results of my terrella experiments. 



Just about the time of the equinoxes the "second sectional line" of the corpuscle-rays round the 

 arth, should, in analogy with the experiments, be most strongly present and as it moreover will fall in 

 he earth's magnetic equatorial plane about 180 degrees from the direction to the sun, it will also fall 

 omewhat in the plane of the ecliptic or near the sun's equatorial plane. 



The experiments referred to concerning the second sectional line, are those described on pages 

 ,60 to 564. The vertical screen used in these experiments consisted principally of two plane 

 iortions which intersected one another at an angle of about 100 in a vertical line. When, therefore, 

 : is recorded that the second sectional line, with magnetising currents 8 and 28 amperes respectively, 

 ell on the screen when its hour-angles were 272 and 265, it must be remembered that the plane part 

 if the screen nearest the terrella and, passing through the magnetic axis had then a length of about 

 92 and 185. 



Uirkeland. The Norwegian Aurora Polaris Expedition, 1902 1903. 79 



